To understand the level of abstraction of the proposed dataset, we first calculate the number of n-grams that appear only in the reference summaries and not in the original texts they summarize [1]}, [2]}.
As shown in Figure REF , 41.4% of words in the reference summaries did not appear in the original text. Additionally, 78.5%, 88.4%, and 92.3% of 2-, 3-, and 4-grams in the reference summaries did not appear in the original text. When compared to a standard abstractive news dataset also shown in the graph (DUC 2002), the legal dataset is significantly more abstractive.
